CHESAPEAKE, Va. — Television evangelist Pat Robertson announced Tuesday that he has decided to enter the Republican presidential race, citing the success of a yearlong petition drive to obtain the names of 3 million people who want him to run.

"There appears to be the substantial support necessary for me to win the Republican nomination and the general election, as well," Robertson said against a backdrop of stacks of petitions piled around him. He said he will officially announce his candidacy on Oct. 1.

There was some confusion about the status of the petition drive, however. Robertson said at the press conference here that while he had obtained 3.3 million names, some of them had been solicited over the telephone. His chief strategist, Marc Nuttle, said later that the campaign had obtained 3 million signatures.

Robertson, 57, began the drive a year ago to test his popularity as a presidential candidate and said at that time that he would not run unless he gathered 3 million signatures by Sept. 17 of this year. People signing the petitions pledged to pray for the campaign, work for it or do both.

Robertson said also that he had raised and spent $10 million in campaign funds, although he has not yet filed a formal report on his finances with the Federal Election Commission.

He said that he would like to campaign without accepting federal funds but "if I have to I will." He said that based on contributions so far, he would be eligible for $5 million in federal funds that match the first individual contributions of $250.

Robertson's campaign, with its foundation among apolitical, "born-again" Christian conservatives, is becoming a troubling enigma to his opponents.

On the one hand, public opinion polls consistently give Robertson high negative ratings. On the other, his organized supporters keep chalking up impressive performances in intraparty skirmishes. One of his latest victories occurred Saturday in Iowa, where he turned out enough followers to finish first in a straw poll organized by the Iowa Republican Party.

In earlier tests of organizational strength, he has done well in Florida, South Carolina and especially Michigan, where his supporters teamed up with those of another Republican presidential candidate, New York Rep. Jack Kemp, in a struggle with Vice President George Bush over the selection of delegates to the Republican National Convention next year.

Another Setback for Bush

The Robertson-Kemp forces combined Tuesday night to deal Bush another setback by persuading the Michigan Republican Party to approve a rule change that bars an estimated 1,100 GOP nominees for city, county and state office from automatically serving as precinct delegates in caucuses next January.

The party ruling restricts participation in the caucuses to just over 9,000 delegates elected in the state's August, 1986, caucuses. The decision in effect denies Bush the backing of party regulars who were supporting his campaign.

Robertson readily admits that his strategy is best suited to caucus states where relatively few people take part in the process and where bands of dedicated activists can score victories against slower moving party regulars.

He does not deny that his toughest test will come in non-caucus states, such as New Hampshire, that lack a strong evangelical base.

"New Hampshire will be the acid test for us," campaign strategist Kerry Moody said. "If we do well there, people won't be able to explain it away. They can't say we sent in the shock troops and rigged the caucus."

Robertson's advisers say his success will depend on his ability to project a moral force that is not identified too closely with a particular religious point of view.

On foreign policy, Robertson said Tuesday that he would campaign against an arms agreement that would not require the Soviets to reduce conventional forces in Europe, make more progress on human rights in their own country, pull back from Afghanistan and end their influence in Central America.

In speaking to audiences of evangelical and secular conservatives in New Hampshire recently, Robertson deplored moral profligacy that included wasteful government spending as well as drug use, divorce and abortion.

"I am dreaming of a time when husbands and wives love each other," Robertson said and then pointed out that divorce is a major cause of poverty among women.

Robertson handles the subject of church and state a bit differently in front of different audiences.

"George Washington referred often to providence. But George Washington never used Christian language publicly," Robertson told a group of New Hampshire Rotarians, suggesting that Washington had set a good example.

Later the same day, speaking to a gathering of evangelicals, he said: "There isn't anything in our history which indicates we ought to separate God from country. How can we ask God's blessing if we constantly slap him in the face?"